UBE3A is maternally expressed in neurons and encodes an E3 ubiquitin ligase named E6-AP. An endogenous antisense transcript of UBE3A, termed UBE3A-ATS, has been identified in humans and mice. UBE3A-ATS functions to suppress paternal Ube3a expression. (Meng et al., Hum Mol Genet. 21:3001-12, 2012).
Angelman syndrome (AS) is a neurodevelopmental disorder mostly attributed to deficiency of maternal UBE3A at 15q11.2, whereas paternal UBE3A is subject to genomic imprinting and silencing in neurons. Patients of Angelman syndrome suffer from developmental delay, speech impairment and seizures. Therapies for Angelman syndrome are limited and mainly focus on symptomatic management. (Williams, C. A. et al., Genet. Med., 12: 385-395, 2010).
Recently, topoisomerase inhibitors currently used in cancer treatment were found to “unsilence” paternal Ube3a expression in both a neuronal culture system and mice. (Huang, H. S. et al., Nature, 481: 185-189, 2012). However, the exact mechanism of unsilencing paternal Ube3a expression remains unknown and topoisomerase inhibitors are fraught with safety concerns because they are known to be non-specific and capable of inducing DNA damage, such as single and double-strand breaks.
Antisense technology is an effective means for modulating the expression of one or more specific gene products and can therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications. Chemically modified nucleosides may be incorporated into antisense compounds to enhance one or more properties, such as nuclease resistance, pharmacokinetics or affinity for a target nucleic acid. In 1998, the antisense compound, Vitravene® (fomivirsen; developed by Isis Pharmaceuticals Inc., Carlsbad, Calif.) was the first antisense drug to achieve marketing clearance from the U.S. Food and Drug Administration (FDA), and is currently a treatment of cytomegalovirus (CMV)-induced retinitis in AIDS patients. For another example, an antisense oligonucleotide targeting ApoB, KYNAMRO™, has been approved by the U.S. Food and Drug Administration (FDA) as an adjunct treatment to lipid-lowering medications and diet to reduce low density lipoprotein-cholesterol (LDL-C), ApoB, total cholesterol (TC), and non-high density lipoprotein-cholesterol (non HDL-C) in patients with homozygous familial hypercholesterolemia (HoFH).